This invention relates in general to a method and apparatus for detecting objects dragging beneath a train as the train travels along a track and, more particularly, to a method and apparatus for detecting objects dragging beneath a train by sensing the force of impact between the object and a stationary impact element which is positioned along the track in the path of movement of the object.
The present invention addresses a long-standing problem in the railroad industry. A variety of objects are typically secured at or near the underside of a train and from time to time some of those objects will become loose or partially detached from the train. For example, the vibration of the train traveling along the track may cause an air hose, a pipe or another object to drag beneath the train. Dragging objects present a potential safety problem which could result in derailment. Moreover, dragging objects may damage switches, tracks, ties and crossings.
To reduce the risk of derailment and other potential damage caused by dragging objects, xe2x80x9cdraggersxe2x80x9d have been used to detect the presence of objects dragging beneath a moving train. As an example, draggers may be placed at 20 mile intervals over long stretches of a railroad track, with additional draggers positioned near road crossings. If a dragging object is detected, the train is stopped so that the object can be secured to reduce the potential for derailment or other problems. The height of the dragger is determined by balancing the risk of not detecting an object (such as an air hose) which is not dragging very far below the bottom of the train against the likelihood of unnecessarily stopping the train numerous times. Draggers are usually set at a height of about one inch below the top rail so that only objects hanging well below the train will be detected. Air hose detectors, on the other hand, typically extend a couple of inches above the top rail. Consequently, air hose detectors are primarily used in railroad yards rather than open stretches of track so that fast-moving trains will not have to make frequent stops to secure low-risk objects.
One conventional dragger rotates on a shaft between a non-impact position and an impact position. A mechanical contact detects an impact when the dragger is forced into its impact position. For example, a contact which is normally open when the dragger is in its non-impact position closes when the dragger moves to its impact position. These draggers are typically biased to return to the non-impact position to avoid the need to manually reset the dragger.
The conventional dragger described above has several drawbacks. Because it relies upon moving parts, it requires considerable maintenance (e.g., lubrication). If the dragger becomes stuck in the impact position, it must be manually reset or it will remain in a constant alarm mode. In colder climates, snow or ice may accumulate on the tracks and inhibit operation of the dragger. To prevent snow and ice build-up, electric pan heaters have been installed around these draggers with limited success. The installation and use of pan heaters is costly and softens the roadbed between ties, which may result in an uneven path for the train. It is also difficult to set and to adjust the minimum force needed to trigger an alarm.
Another conventional approach is to place a brittle metal bar or a wire across the track so that it will break upon impact. This one-shot approach is flawed in that it results in a loss of protection from the time the bar or wire is broken until it is later replaced. A similar approach involves a portable dragger with a metal bar which is often sent flying in an unpredictable direction upon impact. The flight of this metal bar is dangerous to people on the ground and could cause derailment if it lands on the rail. The metal bar sometimes becomes dislodged in response to vibrations from the train, which causes the portable dragger to falsely report alarms. As those skilled in the art will appreciate, trains with xe2x80x9cflat wheelsxe2x80x9d are particularly likely to trigger a false alarm as they travel toward a portable dragger.
Yet another conventional dragger uses audible sensors to detect the presence of an object dragging from a train by sensing the sound or tone which results from the impact between the object and the dragger. This type of dragger is difficult to install and does not perform well in extreme weather conditions. It must be adjusted frequently because the sensitivity of the sensors varies dramatically with temperature changes, and adjustment is difficult due to the indirect means of sensing an impact based on the sound it makes. Moreover, snow and ice dampen the sound from an impact and thus adversely affect the ability of the audible sensors to accurately detect the occurrence of an impact. Consequently, these draggers may not work in snowy and icy conditions without a pan heater.
Another common problem with conventional draggers is that the associated circuitry does not automatically detect faults (e.g., open circuits, short circuits and power failures) in the dragger cable. For example, if a normally closed dragger cable shorts or a normally open dragger cable opens, a fault exists which will prevent the dragger from detecting a dragging object.
Among the several objects and advantages of the present invention may be noted the provision of an improved apparatus and method for detecting objects dragging beneath a train as the train travels along a track; to provide such an apparatus and method which reduces or eliminates false alarms caused by flat wheels; to provide such an apparatus which requires less maintenance than draggers which rely on moving parts; to provide such an apparatus which is more durable than conventional draggers; to provide such an apparatus which performs effectively in snowy and icy conditions without a heater; to provide such an apparatus and method which monitors each sensor cable for faults; to provide such an apparatus with improved troubleshooting capabilities to provide such an apparatus which can be conveniently and economically installed and adjusted; to provide such an apparatus having an impact element which is reversible and interchangeable with other such impact elements; to provide such an apparatus which can conveniently replace conventional draggers having moving parts. These and other related objects of the present invention will become readily apparent upon further review of the specification and drawings.
Briefly, the present invention is directed to an apparatus for detecting objects dragging beneath a train as the train travels along a track. The apparatus of the present invention includes a first stationary impact element adapted to be rigidly supported along the track in a position intersecting the path of movement of the objects to be detected as they are dragged beneath the train so that the objects impact the first impact element. The apparatus also includes a detection circuit having a first sensor coupled with the first impact element for sensing the force of the impacts between the objects and the first impact element.
In another aspect, the present invention is directed to a method of detecting objects dragging beneath a train as the train travels along a track. The method of the present invention includes the step of positioning a stationary impact element along the track in a fixed position intersecting the path of movement of the objects to be detected as they are dragged beneath the train so that the objects impact the stationary element. The method further includes the steps of sensing the force of each impact and generating an output signal if the magnitude of any impact is greater than a predetermined magnitude.